(1) Field of the Invention
This invention relates generally to a draft inducing blower in a furnace, and, more particularly, the invention pertains to an improvement in the blower design that provides internal cooling for a motor that drives the blower.
(2) Description of the Related Art
Blowers to which the present invention is directed are common in the art. Generally, these blowers are located downstream of a combustion chamber or combustion tubes in the furnace, depending upon the style of furnace. The blower draws combustion air into the combustion chamber or combustion tubes, where the combustion air is mixed with fuel and ignited to generate heat for the furnace. The heated exhaust gases are then drawn through a heat exchanger by the blower and discharged from the blower to an exhaust pipe that vents to the outside atmosphere.
The blower generally includes a blower housing and a blower motor installed on the blower housing. The blower housing typically has a side wall, top piece, and bottom piece that define a volute for the blower housing. When the blower is energized, an impeller, operably connected to a shaft of the blower motor, rotates in the volute to draw exhaust gases through an intake hole in the center of the bottom piece and to compress gases in the volute. The impeller draws exhaust gases directly from the combustion chamber or combustion tubes into the blower housing. The pressurized exhaust gases are directed into a discharge exit that extends outward and away from the side wall of the blower housing. The discharge exit is coupled to an exhaust pipe that vents the exhaust gases to atmosphere. In this arrangement, the impeller rotates at a high rate of speed to generate sufficient air flow to draw combustion air into the combustion chamber and combustion tubes and to expel the exhaust gases into the exhaust pipe.
In a typical conventional furnace, the combustion air is drawn into a vestibule of the furnace before it is directed into the combustion chamber or combustion tubes. Generally, the blower motor and blower housing are located in the vestibule with the blower intake in communication with the combustion chamber or combustion tubes. Control electronics for the furnace are also generally located in the vestibule.
During operation of the furnace, temperatures in the vestibule increase and tend to degrade performance of furnace components located in the vestibule. The proximity of the vestibule to the combustion chamber or tubes and the heat generated by the blower motor as the motor runs elevate the temperature within the vestibule. The hot exhaust gases circulating through the blower also contribute to the elevated temperatures in the vestibule. The elevated temperature within the vestibule tends to shorten the life of the blower motor, and electronics and controls located within the vestibule. However, because the blower draws relatively cool air into the vestibule before combustion, the vestibule is generally the preferred place on the conventional furnace for positioning temperature sensitive equipment for the furnace. Additionally, to maintain proper operation of the blower motor during the period of elevated temperature in the vestibule, conventional blower motors utilize an auxiliary fan attached to the rotating shaft of the motor to dissipate the heat generated by the motor.
Although the auxiliary fan usually provides adequate heat removal for the motor, the auxiliary fan has many disadvantages. First, the use of an auxiliary fan on the blower motor increases the size and/or height of the motor assembly, thereby preventing the streamlining of the motor assembly and reduction of the space reserved for the blower in the furnace. Because the auxiliary fan is generally positioned outside of the motor casing, guards and other safety devices must be attached to the motor casing to prevent inadvertent contact with the rotating fan blades during operation. The guard and the fan itself also add cost to the blower motor. The blower motor with an auxiliary fan generates additional noise. Finally, because the motor is positioned in the vestibule, the auxiliary fan recirculates and reuses air in the vestibule. This recirculation and reuse of the air in the vestibule contributes to the elevated temperatures of the vestibule and the associated components positioned therein. Because the motor operates in the vestibule at higher temperatures, the motor must again be upscaled in design, which adds cost to the blower.
Therefore, it is an object of the present invention to provide an improved blower that overcomes the disadvantages of conventional blowers, while providing a blower that cools the blower motor without the use of an auxiliary fan attached to the blower motor.